The present invention relates to a semiconductor laser apparatus to be used in the fields of optical information processing, optical measurement, optical communication, and the like.
The following is a description of semiconductor laser apparatuses of prior art, based on the drawings.
First Prior Art
FIG. 13 is a section view illustrating the arrangement of the semiconductor laser apparatus of first prior art. As shown in FIG. 13, the apparatus comprises a semiconductor laser element 101 which is composed of a compound semiconductor consisting of GaAs or the like, a laser mount 102 which is disposed beneath the semiconductor laser element 101 so as to position the element 101, and a heat sink 103 which is disposed beneath the laser mount 102 so as to dissipate the heat generated by the semiconductor laser element 101 through the laser mount 102. These members 101, 102, and 103 are mutually secured through hot contact bonding with the use of solder or the like. Since the semiconductor laser element 101 and the laser mount 102 are different in coefficient of thermal expansion, stress is generated in the laser mount 102 with respect to the semiconductor laser element 101. To reduce this stress, the laser mount 102 is generally made of silicon or the like of which difference in coefficient of thermal expansion with respect to the semiconductor laser element 101 is small.
Second Prior Art
FIG. 14 is a section view illustrating the arrangement of the semiconductor laser apparatus of second prior art, which is disclosed in Japanese Laid-open Patent Application No. 6-203403, and which comprises a semiconductor laser element and circuit elements including an optical sensor and a signal processing circuit, all of them being provided on the substrate. As shown in FIG. 14, the apparatus comprises a heat sink 103, a silicon semiconductor substrate 112, which is disposed on the heat sink 103 and has a concave portion on the top thereof, the concave portion having inner walls so inclined as to form an inverse trapezoid, and a semiconductor laser element 101, which is disposed on the bottom surface of the concave portion of the semiconductor substrate 112. These members 103, 112, and 101 are mutually secured through hot contact bonding with the use of solder or the like.
Formed on a top of the concave portion of the semiconductor substrate 112 is an optical sensor 112a, which detects a light 104 externally incident thereupon. A reflection mirror 112b, which reflects a laser light 105, is formed on that inclined inner wall of the concave portion in the semiconductor substrate 112 which is located on the side of the optical sensor 112a. The laser light 105 is emitted from the semiconductor laser element 101 in a direction substantially parallel with the main surface of the semiconductor substrate 112 and reflected by the reflection mirror 112b in a direction substantially vertical to the main surface of the semiconductor substrate 112. A laser light sensor 112c, which monitors the operation of the semiconductor laser element 101, is formed on that inclined inner wall of the concave portion of the semiconductor substrate 112 which is located on the side opposite to the optical sensor 112a. By setting the angle of inclination of the inner walls of the concave portion so that the optical axis of the laser light 105 reflected by the reflection mirror 112b is substantially parallel with the optical axis of the externally incident light 104, the semiconductor laser apparatus can be efficiently combined with an external optical device. The semiconductor substrate 112 is further provided with such unillustrated members as an amplifier circuit for amplifying a signal supplied from the optical sensor 112a and outputting the amplified signal, an operating circuit for performing operation on the signal supplied from the amplifier circuit, and a drive circuit for driving the semiconductor laser element 101.
In the second prior art, too, the semiconductor laser element 101 is secured to the semiconductor substrate 112 which is made of silicon of which difference in coefficient of thermal expansion with respect to the semiconductor laser element 101 is small. Accordingly, the stress of the semiconductor substrate 112 with respect to the semiconductor laser element 101 is small.
Third Prior Art
FIG. 15 is a section view illustrating the arrangement of the semiconductor laser apparatus as third prior art. As shown in FIG. 15, a laser mount 113, which comprises an upper silicon layer 113a and a lower diamond layer 113b secured to each other, is disposed between a semiconductor laser element 101 and a heat sink 103. The upper silicon layer 113a is made of silicon having small difference in coefficient of thermal expansion with respect to the semiconductor laser element 101 and secured to the semiconductor laser element 101. The lower diamond layer 113b is made of diamond having thermal conductivity higher than silicon and secured to the heat sink 103. The upper silicon layer 113a functions to reduce the stress of the laser mount 113 with respect to the semiconductor laser element 101 while the lower diamond layer 113b functions to improve heat dissipation of the laser mount 113.
Fourth Prior Art
In the first to third prior art, the laser mount or the substrate which is in contact with the semiconductor laser element, is composed of a silicon semiconductor or the like having a small difference in coefficient of thermal expansion with respect to the semiconductor laser element. In addition to them, another method has been proposed to reduce the stress and improve the heat dissipation by using a material such as silicon carbide (SiC), aluminum nitride (AlN), or diamond (C), which has a small difference in coefficient of thermal expansion with respect to the semiconductor laser element and which is higher in thermal conductivity than a semiconductor (Japanese Laid-open Patent Application No. 2-138785).
However, the semiconductor laser apparatuses of the first and second prior art have a problem as follows. The laser mount 102 or 112, to which the semiconductor laser element 101 is secured, is composed of a semiconductor made of silicon or the like having relatively low thermal conductivity. Accordingly, the heat dissipation is so poor that the semiconductor laser element 101 is susceptible to heat, which disadvantageously shortens the expected lifetime of the semiconductor laser element 101.
The semiconductor laser apparatus of the third prior art has problems as follows. The upper silicon layer 113a and the lower diamond layer 113b, which compose the laser mount 113, come off from each other due to stress resulting from the difference in coefficient of thermal expansion therebetween. This results in insufficient heat dissipation of the semiconductor laser element 101, which causes the semiconductor laser element 101 to be deteriorated due to heat. In addition, more component elements are needed to separately produce and assemble the upper silicon layer 113a and the lower diamond layer 113b, and also a special machining device such as a laser cutter is required for the difficult machine of a sheet-like diamond, which increases the production cost.
The semiconductor laser apparatus of the fourth prior art also has a problem that the use of silicon carbide, aluminium nitride, diamond, or the like which is difficult to be machined due to its hardness increases the machining and production costs.